condition mean min max ZT0-3 7.671887 7.671887 7.671887 ZT4-7 8.1596425 8.1596425 8.1596425 ZT8-11 7.755831000000001 7.755831000000001 7.755831000000001 ZT12-15 7.671887 7.671887 7.671887 ZT16-19 7.0271609999999995 7.0271609999999995 7.0271609999999995 ZT20-23 8.050769500000001 8.050769500000001 8.050769500000001